Part of the operation of a nuclear power plant is the removal and disposal of irradiated nuclear fuel assemblies. Most early reactors were originally built to store from three to five years capacity of irradiated fuel assemblies in a storage pool. From the storage pool, the irradiated fuel assemblies could be reprocessed or sent to long-term storage. However since 1977, due to uncertainties in the federal policies relating to reprocessing of irradiated fuel and also in the establishment of permanent irradiated fuel dumps, on-site irradiated fuel storage facilities have been stressed to their capacity for storing these irradiated fuel assemblies. To prevent the forced shutdown of these plants due to the overcrowding of storage pools, a number of near-term irradiated fuel storage concepts have been developed and/or utilized.
The first among these is the development of high density irradiated fuel racks which can be installed in existing storage pools. This type of rack generally increases the storage capacity of a pool by two to three times. Unfortunately, this re-racking is not always sufficient to provide storage capacity for the life of the plant.
Another possible solution is fuel rod consolidation or compaction. In this solution, the individual fuel rods are separated from the fuel assemblies and are placed into canisters in a closely packed configuration, with the canisters being stored in storage pool racks. This option is limited to a low percentage of existing plants because of the structural load limitations on storage pool foundations.
Nuclear energy plants have considered various types of dry storage devices for irradiated fuel. There are basically three types of dry storage facilities. The first includes a cask storage system which is an above-ground monolithic structure with thick walls comprised of a shielding material such as steel, nodular cast iron, depleted uranium, lead, or concrete surrounding a central internal cavity which contains one or more fuel bundles. Due to the size and weight of the typical storage cask, only about half of the utilities can implement this type of storage without considerable expense. This system can be implemented either with a cask which has space for a multiplicity of fuel bundles or an above-ground silo which is used for one fuel bundle.
Another dry storage concept is the use of a dry well, which is also known as caisson storage. This concept involves using lined holes in the earth which are deep enough to accommodate the irradiated fuel and a shielding plug. The dry well relies on the properties of the surrounding earth for shielding and heat reduction. This type of storage requires considerable land space above the flood plane.
Another dry storage concept is the use of air-cooled vaults. This system is also referred to as canyon storage. The vaults consist of shielded structures with storage racks into which the irradiated fuel is placed and around which air can circulate to remove irradiated fuel decay heat. The vaults are located below ground, as are the dry wells. As with the dry wells, this type of storage tends to be relatively expensive.
All of the above dry storage systems store the fuel in a vertical position and thus require, in addition to all the transfer and storage equipment, a large capacity crane for lifting the fuel and surrounding casks from the transfer vehicles into the storage devices.
The present invention is directed to overcoming the problems of the prior art.